Roller rockers useless?

[MACE]

Nice resources there vxcalais_01

I can assure you the duration becomes much more noticeable when you say go from stock to a 2.15:1 ratio rocker, by the way the car idles

 

[Immortality]

Higher ratio rockers and net cam duration • Speed Talk

There's a good graph on there to explain what i am talking about. It is not possible for it to lift higher and not be any change to the duration. In relation to the cam the valves are not lifting in a direct up and down movement at only one point, its across the whole lobe. I hope this explains what i am trying to say.


Higher Ratio Rocker Arms

Above is another favorite i have read that explains this theory.

not to be picky, but to quote from the above link that you have given

The cam is rated at some duration at .050 lifter/tappet rise. This of course cannot be changed and will remain the same regardless of the rocker arm ratio

What happens to valve open time with the higher ratio rockers? Because the higher ratio rocker lifts the valve to a higher point in the same time period, it has to lift both quicker and steeper. As the valve begins to open at the same point regardless of rocker ratio, and it opens at the same time as the cam lobe, the duration of the valve opening in crankshaft degrees at the initial opening and closing points is identical to the cam lobe duration

as the graph clearly shows from your link, the point that the valve lifts off the seat stays the same regardless of rocker ratio (which i have said all along)

what does clearly increase is the area under the curve, or the effective area that the cylinder can breathe (when the valve is open) and as can be clearly seen on the graph, when higher ratio rockers are used you increase the overlap, the period the both the intake and exhaust valve are open and this has a marked notice on the way a engine idles.

As the valve begins to open at the same point regardless of rocker ratio, and it opens at the same time as the cam lobe, the duration of the valve opening in crankshaft degrees at the initial opening and closing points is identical to the cam lobe duration.

However, because of the quicker and steeper opening/closing rates, the valve open time is greater from any point after initial opening when a higher ratio rocker is used.

now this is where it gets interesting

How much more duration? I devised a method to actually measure it. As a standard lobe measuring point is .050 lifter rise, and lobe lifts are normally specified with 1.5 rocker ratio, that means the valve will always be at .075 when the lobe reaches .050" lift (when a 1.5 rocker is installed). By using the .075 point, and determining where it occurs in relationship to the crank in degrees, a yardstick is provided from which to reference any different rocker ratios. As expected, a higher ratio rocker will allow the valve to reach the .075 lift point earlier in the lift cycle (and later in the closing cycle). As the .075 valve lift point is the industry standard when specifying cam duration (1.5 standard rocker ratio X .050 tappet/lifter rise), it becomes a valid reference point.

this is all very nice, however we are not comparing apples with apples here because the rocker ratio has changed however what has not changed is the seat to seat duration of the cam (or the point where the valve begins to lift off the seat and when it sets back down on the seat). as most people will be aware cams normally have 2 duration numbers, seat to seat and @ .050" lift. lets say for arguments sake that (when using a 1.5:1 ratio rocker as standard and note that not all engines use this as standard ratio as alluded to in the link) no effective flow is established until the valve has lifted .075" (.050" lobe lift multiplied by the 1.5:1 rocker ratio) off the seat (just using this figure as it was used in the example in the link) then changing to a higher rocker ratio the valve will reach the .075" lift value sooner there by allowing the cylinder to effectively breathe sooner. it could be argued that we have therefore increased the duration where in reality all we have done is lift the valve of the seat faster. so to give it a better description what we could say is that the "effective duration" of the cam has increased (by virtue of the fact that we have lifted the valve faster of the seat)

As the .075 valve lift point is the industry standard when specifying cam duration (1.5 standard rocker ratio X .050 tappet/lifter rise), it becomes a valid reference point.

1.5 ratio rockers may be the standard for old style Chevy engines, however not for any recent Holden engine (or engines used in a Holden) i.e. 308/304 standard rocker ratio is 1.6/1.65
buick 3800 V6 standard ratio is 1.6
ecotec V6 standard ratio is 1.65
LSx standard ratio 1.7

so using the above standard rocker ratio's the .075" lift is different for every engine and there for not a valid reference point and the reason cam duration is always measured at the cam and not the valve

 

[vxcalais_01]

immortality, its the theory that counts. I believe it is valid when going from 1.65 to 1.95 and above etc. I explained myself already in post 30 and earlier. You were explaining the rockers characteristics more like a vertical only performance in your previous posts. The physical duration of the cam cannot be changed, neither the lift on the lobes profile etc, but the higher ratio rockers can relay the change to the valves and alter the characteristics. This is my understanding of it. If i am wrong so be it.

Like in my original post to provide info to the OP, there are benefits in using both a performance cam and higher ratio rockers.

"Higher ratio rocker arms open the valve faster, higher, and hold it open for a much greater total period of time as compared to lower ratio units. Does this cause more stress on the valve train? There will be more pressure on the cam lobes due to the friction and pressure caused by the higher lift and resultant greater spring load. However, as compared to providing the same higher lift and effective longer duration with a more radical cam and even stiffer springs, the higher ratio rockers may create less total valve train stress. And such a cam lobe would be very aggressive and would require much heavier springs to keep the lifter from flying off the lobe. Very radical lobes will also add more side stress on the lifters/bores and could possibly cause lifter bore failure. The added pressure on the studs from either higher ratio rockers, or more radical lobe, will be well within the capabilities of modern after market studs."

I believe the above summary from the site is excellent and relevant theory to many engines. At the end of the day its a Pontiac site as well which used to be a GM brand. Anyways, enough from me.

 

[Immortality]

immortality, its the theory that counts. I believe it is valid when going from 1.65 to 1.95 and above etc. I explained myself already in post 30 and earlier. You were explaining the rockers characteristics more like a vertical only performance in your previous posts. The physical duration of the cam cannot be changed, neither the lift on the lobes profile etc, but the higher ratio rockers can relay the change to the valves and alter the characteristics. This is my understanding of it. If i am wrong so be it.

Like in my original post to provide info to the OP, there are benefits in using both a performance cam and higher ratio rockers.

I believe the above summary from the site is excellent and relevant theory to many engines. At the end of the day its a Pontiac site as well which used to be a GM brand. Anyways, enough from me.

i try to keep my explanations simple. so my earlier statements are correct. theory is nice but what happens in real practise is what counts. i believe i have explained that very well using the text that you supplied.

so in summary, the seat to seat duration stays the same (no matter what the rocker ratio). once the valve has lifted off the seat the valve lift will be higher at any given time (when using a higher then standard ratio rocker) until the valve sits back down on the seat. so what we have increased by using the higher ratio rocker is the total average lift which increases total average flow (you will see head porters talk about this value a lot rather then just referring to peak flow).

you will also see if you check other posts of mine on both this forum as well as others that i have been a advocate for the use of both cams and high ratio rockers to get the max attainable lift as limited by your head configuration (which is normally dictated by your valve springs, valve stem seals and relevant machining).

all I'm doing here is trying to make sure that people have a clear understanding of what effect different parts have on the engine.

the problem with forums is that it is very easy to create myths. basically somebody makes a comment/statement, another forumite reads that comment/statement and not knowing whether it is true or not then repeats the previous comments/statements else where. this effect then snow balls and soon enough something that could be a complete work of fiction seems to have become fact spread through forums (not that i'm saying that here). this is where a good healthy debate comes in very handy as people then get to see multiple opinions and can decide for themselves what they want to believe and what to ignore (a good debate can also make what can otherwise be a boring/dull day interesting and keeps the grey matter working

 

[vxcalais_01]

Thanks immortality . I agree with your information on the rockers and cam and as well as being as accurate as possible on forums as like you said we need to be as accurate as possible when using terms. If i used the term duration, i am envisioning the valve and rocker more than anything, even though duration is a camshaft terminology and a field i am still learning about. Unfortunately the net is limited in how one can put an explanation across. Sorry mate.

 

[HamaTime™]

Despite not being involved in your debate/conversation. Thanks for the in depth explanations. I understand alot more about how it all works.

Rep given to both of you for your explanations.

 

[Raptorsc]

I will also back up the other comment about CHIPTORQUE

There is simply no company who modifies the stock ECU in the VU, VX or VY V6s better than CT, without them a lot of stuff would be even harder than it already is.

Some of the other comment is probably justified, sometimes things don't always go to plan with tunes and I have had my share of that kind of experience also a long while ago

 

[vxcalais_01]

Thanks HamaTime

 

[GenReaper]

Rockers affect duration as well it has to, theres no way the valve can only slap up and down at that point of lift, it has to ride along the duration curvature as well if you know what i mean. But its not as much as what can be designed into a cam. High ratio rockers and cam are the best, as both have strengths that the other other hasn't.

lol i dont know what trade school you went too because you are totaly wrong about that. The cam effects duration, not the rockers.

 

[0081]

I got told today that any high ratio roller rockers are useless because from VR models and upwards come factory with them? And even if i did get them i'd have to do cam work.
And i was told this by a mechanic, who would presumebly want my money.

Is he honest or in need of a mental home?

Getting back to your orginal question i would say that when you said roller rockers to him you lost him a bit as yes the VR's do come with roller rockers but you ment some with a higher lift.